1. Field of the Invention
The present invention relates generally to fuel injection systems for internal combustion engines and, more particularly, to fuel injectors which are suitable for dispensing an ultra-high pressure fuel into engine cylinders and capable of being electronically controlled to regulate the quantity of fuel injected and the injection timing.
2. Description of the Prior Art
In fuel injection systems, it is desirable that the fuel be injected at an ultra-high pressure as compared with the ordinary injection pressure. Ultra-high pressure injection ensures that fuel injection under a high engine load takes place within a shortened time period and that the fuel particles are atomized to an enhanced degree, thereby reducing the amount of harmful exhaust emissions. Ultra-high pressure injection may be achieved by the use of a servo multiplier pump which is capable of pressurizing the fuel to an extremely high pressure, e.g., more than 600 kg/cm.sup.2.
It is also desirable that the metering of the fuel and regulation of injection timing be performed with an improved accuracy in accordance with various engine parameters, such as engine speed, engine load, coolant temperature, and intake air temperature. This may be achieved by electronic control methods wherein an electronic control unit (ECU) is used to calculate the timing and period of the injection according to the engine parameters, and to issue signals to control solenoid-operated injection nozzles of the fuel injectors. However, in ultra-high pressure fuel injectors, needle valves are subjected to a very high pressure, and thus, the solenoids must be designed to generate outputs sufficient to control the needle valves. However, if the size of the solenoids is increased to give increased outputs, the response of the solenoids will become unacceptable.